Studies in this and other laboratories have shown that a ubiquitous multi-functional calcium binding protein, calmodulin (CaM) has the potential to serve as the mediator of calcium second messenger signals in eucaryotic cells. CaM can act as a calcium dependent regulator of cyclic nucleotide metabolism, the membrane Ca2 ion-pump and can activate a number of highly specific protein kinases including those which directly modulate motile processes in animal cells. The multiple activties of CaM are therefore perfectly suited to regulating the entire stimulus-response-relaxation cycle in excitable tissues. Studies are proposed in this application to significantly broaden our understanding of the phylogenetic distribution of CaM including structural alterations which have occurred during its evolution. Detailed analyses of CaM from a number of vertebrate species will be completed. Structural analyses of CaM from the invertebrate Renilla reniformis will also be completed during the coming year. The structural and functional properties of CaMs recently isolated from the C.elegans and Physarum polycephalum will be examined including complete physicochemical characterization, tryptic and CNBr peptide mapping and determination of complete functional properties. These studies will complement detailed analyses of the exact domains within bovine brain CaM responsible for calcium dependent interaction with CaM-regulated enzymes and antipsychotic drugs. These studies should provide a detailed understanding of the molecular mechanisms through which fluxes in the divalent cation, Ca2 ion, regulate motile processes in eucaryotic cells as well as a detailed knowledge of the evolutionary origins of the stimulus-response system.